1. Field of the Invention
The present invention relates to an accumulator used for, for example, hydraulic circuits in hydraulic control apparatuses, specifically relates to a securing structure for hydraulic ports with respect to sealed vessels (shells) for hydraulic fluids and gases, and relates to a protecting structure for a partitioning member installed therein.
2. Background Art
The accumulator such as the above generally comprises a cylindrical shell partitioned into a gas chamber and a hydraulic chamber by a bellows. The pressure variation of the hydraulic fluid flowing into the hydraulic vessel is accommodated by the expansion and compression of the gas in the gas chamber according to the elastic motion of the bellows. The accumulator is widely used in devices such as a hydraulic circuit in automobiles for effectively inhibiting pulsation in the hydraulic fluid flowing therein.
In FIG. 5, an example of a conventional accumulator is shown, and reference numeral 80 is a cylindrical shell which forms a sealed vessel by joining a bottom shell 81 and a cap shell 82. Reference numeral 83 is a metallic bellows assembly partitioning the interior of the shell 80 into a hydraulic chamber 91 and a gas chamber 92. Reference numeral 93 is a port comprising a flow path 93a for communicating a hydraulic circuit (not shown) and the hydraulic chamber 91. The bellows assembly 83 forms the hydraulic chamber 91 therein, and comprises bellows 84 elastically moving in the axial direction of the shell 80, and a bottom seal 85 and a bellows cap 86 joined to both ends of the bellows 84. The bottom seal 85 is joined to the cap shell 82.
The bellows cap 86 is a free end of the bellows assembly 83. The circumference of the bellows cap 86 is mounted with a circular bellows guide 87 which slides with the inner surface of the shell 80 so as to guide the elastic movement of the bellows 84 in the axial direction.
The axial length of the bottom shell 81 is longer than that of the cap shell 82. The joining portion of the shells 81 and 82 approximately faces the bellows 84 even if the bellows 84 is in the most contracted condition.
In such an accumulator, when the hydraulic fluid flows into the hydraulic chamber 91 via the flow path 93a and the pressure of the hydraulic fluid exceeds the gas pressure in the gas chamber 92, the bellows 84 expands, and the gas in the gas chamber 92 is compressed. In contrast, when the hydraulic fluid pressure in the hydraulic chamber 91 is below the gas pressure in the gas chamber 92, the bellows 84 is contracted and the gas in the gas chamber 92 is expanded. Due to the expansion and compression of the gas in the gas chamber 92, the variation of the pressure of the hydraulic fluid in the hydraulic circuit is accommodated and pulsation thereof is inhibited. The two-dot chain line in FIG. 5 shows the position of the bellows cap 73 when the bellows assembly 70 is in the most expanded condition.
The port 93 in the conventional accumulator is joined to the cap shell 82 by projection welding, or the like, which is one type of resistance welding. Welding produces sparks in some cases, and splashed material adheres to the inner surface of the port 93 and the cap shell 82, thereby contaminating therein. When the accumulator is assembled with the contamination, the hydraulic fluid is contaminated and results in malfunctioning of the accumulator. Although cleaning is performed to remove the contamination, it is difficult to completely remove the contamination since there are portions where the cleaning is not easily performed. Furthermore, the cleaning is labor intensive, and the production efficiency is decreased.
In assembly of the conventional accumulator, the bottom shell 81 is welded to the cap shell 82 after joining the bellows assembly 83 to cap shell 82 by welding. Similarly in this case, when the shells 81 and 82 are welded by projection welding, sparks are emitted to the interior of the shell 80, and the bellows 84 may be damaged. Although the service life of the bellows is shortened when the bellows 84 is damaged, it cannot be ascertained whether the bellows 84 is damaged since it is contained in the shell 80, and the normal operation of the accumulator cannot be ensured.
An object of the present invention is to provide an accumulator in which contamination of the interior thereof due to sparks emitted in welding a port can be inhibited and the production efficiency can be improved.
Another object of the invention is to provide an accumulator in which damage to a bellows due to sparks emitted in welding shells can be inhibited and the normal operation of the accumulator in over the long term can be ensured.
The present invention provides an accumulator comprising: a cylindrical shell including a cylindrical portion; a partitioning member for partitioning the interior of the shell into a hydraulic chamber and a gas chamber; and a port including a hydraulic fluid flow path for communicating the exterior of the shell and the hydraulic chamber. Variation of pressure of a hydraulic fluid flowing into the hydraulic chamber is accommodated by expansion and compression of a gas in the gas chamber according to expansion and contraction of the partitioning member. The port is approximately airtightly inserted into the cylindrical portion of the shell, and is welded to an outer circumference of the cylindrical portion by means of welding.
According to the invention, the port is approximately airtightly press fitted into the cylindrical portion of the shell, and the inner surface of the cylindrical portion and the outer surface of the port are closely contacted to each other. Therefore, the outer ridge portion of the cylindrical portion is isolated from the interior of the shell. As a result, when sparks occur during welding, the sparks are not emitted into the interior of the shell, and the interior of the shell is not contaminated by splashing of the sparks. Therefore, the contamination in the shell can be easily controlled and the production efficiency can be improved. Furthermore, even if sparks are emitted in the shell the sparks remain in the gas chamber and do not enter into the hydraulic chamber, so that the system including the hydraulic circuit to which the accumulator is connected is not contaminated by splashing of the sparks.
According to the preferable feature of the invention, in which the overall length of the accumulator can be shortened, the cylindrical portion is projected into the interior of the shell. Several kinds of forming method can be applied to the feature, but burring in which a through hole is formed in the shell and a punch having larger diameter than that of the through hole is press fitted thereinto is preferable.
The partitioning member may comprise a fixed portion and a movable portion mounted to the fixed portion via an elastic member, which corresponds to the bellows assembly 83 in the conventional accumulator in FIG. 5. The fixed portion, the elastic member, and the movable portion correspond to the bottom seal, the bellows, and the bellows cap respectively. It is preferable feature that the fixed portion is integrally formed with the port. Heretofore, the fixed portion (bottom seal) has been joined to the inner surface of the cap shell, so that sparks occurring in welding results in problems of contamination similarly in the port. However, by integrating the fixed portion with the port, the fixed portion needs not to be welded to the cap shell, and the problems due to the sparks can be solved.
According to another preferable feature of the invention, the shell comprises plural divided shell bodies joined to each other. The partitioning member includes a guide for sliding on an inner surface of the shell so as to guide the expansion and contraction of the partitioning member along an axial direction thereof. The joined portion between the divided shell bodies is positioned outside the region where the bellows guide moves. The guide slides within an inner surface of one divided shell body. According to the feature, even if a step is formed at the joined portion of the divided shell bodies (boundary between both), the guide can slide smoothly with no influence from the step, and is not damaged by the joined portion, so that durability thereof can be improved.
According to another aspect of the invention, the invention provides an accumulator comprising: a cylindrical shell including plural divided shell bodies joined to each other in an axial direction thereof; a partitioning member for partitioning the interior of the shell into a hydraulic chamber and a gas chamber, the partitioning member expanding and contracting in the axial direction of the shell; and a guide provided at a free end of the partitioning member, the guide guiding the expansion and contraction of the partitioning member along an axial direction thereof is provided. Variation of the pressure of a hydraulic fluid flowing into the hydraulic chamber is accommodated by expansion and compression of a gas in the gas chamber according to expansion and contraction of the partitioning member. A protecting member is provided between a joined portion of the divided shell bodies and the partitioning member so as to screen both.
The divided shell bodies correspond to the bottom shell and the cap shell respectively, and the partitioning member corresponds to the bellows assembly in the conventional accumulator in FIG. 5. According to the invention, the divided shell bodies are joined to each other by joining means such as projection welding. Sparks occurring in the welding are blocked by the protecting member and cannot strike the partitioning member. Therefore, damage to the partitioning member is prevented and a long service life thereof is ensured, and normal operation of the accumulator can be ensured.
According to the specific feature of the protecting member, a sleeve coaxially aligned with the shell along the inner surface of the shell can be applied. The sleeve extends overall region where the guide moves according to the expansion and contraction of the partitioning member, and the guide slides on a inner surface of the sleeve. According to the feature, the guide moves smoothly sliding on the sleeve, and the partitioning member usually operates in normal manner.
According to another specific feature of the protecting member, it may be a ring-shaped member covering an inner surface of the joined portion of the divided shell bodies. In this case, the ring-shaped member is preferably positioned outside the region where the guide moves, and the guide slides within an inner surface of one divided shell body. According to the feature, even if a step is formed between the divided shell bodies and the ring-shaped member (boundary between both), the guide can slide smoothly with no influence from the step, and the partitioning member can usually operates in normal manner.